unknown piston

My dad is building an 85cc race engine based on an XR75 (post 1976), it is for a friend who will race it at a moped racing club.
This guy brought over a lot of parts to build with, including a big bore piston.
I like this piston, for the 50mm bore that is was originally built for, this one is a 50,75mm bore, 3rd oversize.
This has a 13mm piston pin, just like xr75.
But this piston didn't have any original box, or any markings, so I don't know what it is.

Can you help me identify this piston????

50mm standard bore
13mm piston pin
And very distinctive valve indentations.
But I can't even be sure it is honda, it might be something else.
If you have any idea what this is, please send me an email.